1. Field of the Invention
In general, the invention relates to methods of using polymer foam absorbent materials in wound dressings.
2. Description of Related Art
Since time immemorial, the standard dressing for a wound—the material used to cover a wound, protect it, and absorb blood and other exudates—has been cotton or cotton gauze. Cotton, itself a natural cellulose polymer, is cheap, plentiful, absorbent, and relatively easy to sterilize. Cotton gauze, in pads and rolls, is extremely common in first aid, ambulance, and hospital settings.
Despite its ubiquity, cotton gauze has serious drawbacks. For example, while it is absorbent, it will not draw and sequester fluids and other exudates away from a wound, and it may thus allow bacteria and other harmful elements to remain in contact with the wound and the patient's skin. On a more practical level, once used, cotton gauzes tend to harden and stick to wounds, making them painful to remove and presenting the possibility that removing a used bandage may cause damage or impede healing.
In recent decades, doctors and scientists have come to understand the healing process better. For example, it is now known that moisture is helpful in revascularization and other stages of the healing process, and that it may be helpful if the edges of a wound are kept dry while the interior of the wound is kept moist. However, even though the understanding of the process has improved, chronic wounds, like decubitus ulcers, pressure sores, venous stasis ulcers, infected wounds, deep and open surgical incisions, and burns still present long-term problems and require special care. These chronic types of wounds can require weeks or months to heal, and can easily become infected or cause other complications if not treated adequately. Moreover, there are widely varying opinions on the proper treatment protocols.
While caring for chronic wounds is difficult, and standards of care are still evolving, there is evidence that treatments like negative pressure wound therapy (NPWT) can speed healing. In NPWT, a special, sealed dressing is connected to a pump. The dressing may be, for example, an open-celled foam with an average cell size of greater than about 400 μm that is present to act, essentially, as a filter for the pump—it is typically rigid enough that it will not collapse into the pump, and its cells and structure allow fluid to flow through it under vacuum. When the pump is activated, sub-atmospheric pressures are maintained on a wound. Most commonly, negative pressures between −10 and −125 millimeters of mercury (mm Hg) are used.
While treatment protocols may vary considerably, it has become clear that wound dressings play an important role in wound healing, and scientists and engineers have risen to the challenge of creating more sophisticated materials to use as dressings. For example, moist dressings made with hydrocolloids and hydrogels are known, as are dressings made with polymer foams.
Materials have also been developed for absorptive applications other than wound dressing. For example, the Procter and Gamble company of Cincinnati, Ohio has created an open cell, collapsed polymer foam material, marketed as INFINICEL® in the United States, that is sold primarily for use in menstrual pads. This material, made by polymerizing a high internal phase emulsion (HIPE), is highly absorbent, lightweight, and flexible. In particular, U.S. Pat. No. 5,795,921 to Dyer et al., which is incorporated by reference herein in its entirety, discloses formulations and methods for making this kind of polymer foam such that it has pore sizes appropriate for capturing blood and menses.
The Dyer patent does mention briefly that these types of materials can be used in wound dressings, but does not offer any specific guidance on how they might be used.